Group 2,7 and Redox Flashcards
State and explain the following trend for group 2 elements; atomic radius, first ionisation energy, melting point
Atomic radius increases down the group as the number of shells/energy levels increase. First ionisation energy decreases down the group as shielding increases so the attraction between the nucleus and outer electron decreases. Melting point decreases (except magnesium) because the size of the positive ions increases, and this creates weaker attraction to the delocalised electrons (i.e. weaker metallic bonding).
Explain why group 2 metals have a smaller atomic radius than the preceding group 1 metal
The group 2 metals have a greater nuclear charge/more protons than the previous group 1 metal, but shielding remains the same, so there is stronger attraction between the nucleus and outer electrons. This draws them in slightly closer.
Explain why the second ionisation energy of a group 2 metal is higher than its first ionisation energy
The electron is being removed from a positive ion so there is greater attraction to the electron being removed.
Explain why the third ionisation energy of a group 2 metal is much higher than its second ionisation energy
The third electron is removed from a shell that is closer to the nucleus (as well as being an increasing positive ion). This means that there is even more attraction between the nucleus and electron being removed.
Describe how titanium is extracted from its ore. Write two equations in your answer.
The main titanium ore contains titanium(IV) oxide, TiO2.
The titanium oxide is first reacted with chlorine and carbon to form titanium chloride, TiCl4, and carbon monoxide.
TiO2 + 2Cl2 + 2C à TiCl4 + 2CO
The titanium chloride is then reduced to titanium by reaction with magnesium.
TiCl4 + 2Mg à 2MgCl2 + Ti
Write an equation to show how the following group 2 metals react with water (and steam for Mg) and state the pH of resulting solution; magnesium, calcium, strontium,barium
Mg(s) + 2H2O(l) à Mg(OH)2(s) + H2(g)
It produces a solution of pH 10
Magnesium with steam:
Mg(s) + H2O(g) à MgO(s)+ H2(g)
Ca(s) + 2H2O(l) à Ca(OH)2(aq) + H2(g)
It produces a solution of pH 11.
Sr(s) + 2H2O(l) à Sr(OH)2(aq) + H2(g)
It produces a colourless solution of pH 12.
Ba(s) + 2H2O(l) à Ba(OH)2(aq) + H2(g)
It produces a colourless solution of pH 13.
What and explain the trend in reactivity of group 2 metals
Reactivity increases down the group as the atomic radius/shielding increases so there is less attraction between the nucleus and outer electrons. This means it becomes easier to lose an electron and react.
What is the trend in the solubility of group 2 hydroxides?
The group 2 hydroxides become more soluble as you go down the group.
What are two uses of group 2 hydroxides
Magnesium hydroxide (milk of magnesia) is used to treat indigestion or as a laxative. Calcium hydroxide (slaked lime) is used to neutralise acidic soil.
What is the trend in the solubility of group 2 sulfates
The group 2 sulfates become less soluble as you go down the group.
Describe the chemical test for sulfate ions
Add barium chloride/nitrate. A write precipitate of barium sulfate is formed if sulfate ions are present. Ba2+(aq) + SO42-(aq) à BaSO4(s)
State and explain the medical use of barium sulfate
Barium sulfate (barium meal) can be shallowed to show the digestive tract under x-ray
What are the states and appearances of the group 7 elements at room temperature?
F2 = pale green gas, Cl2 = dense green gas, Br2 = volatile orange liquid, I2 = grey solid, purple vapours when heated.
Describe the structure and bonding of the group 7 elements.
Covalent bond, simple covalent molecules.
State and explain the following trends of the group 7 elements; atomic radius, melting/boiling points, electronegativity, first ionisation energy.
Atomic radius increases down the group as the number of shells/energy levels increases. Electronegativity decreases down the group as the bonding pair of electrons becomes further from the nucleus and experience less attraction. First ionisation energy decreases down the group as the outer electrons from the nucleus becomes further from away/experiences less shielding so becomes easier to lose.
Write a balanced equation for a displacement reaction involving a halogen and a halide. Turn this equation into an ionic equation
Cl2(aq) + 2KBr(aq) à 2KCl(aq) + Br2(aq) (yellow solution)
Cl2(aq) + 2Br-(aq) à 2Cl-(aq) + Br2(aq)
Cl2(aq) + 2KI(aq) à 2KCl(aq) + I2(aq) (brown solution)
Cl2(aq) + 2I-(aq) à 2Cl-(aq) + I2(aq)
Br2(aq) + 2KI(aq) à 2KBr(aq) + I2(aq) (brown solution)
Br2(aq) + 2I-(aq) à 2Br-(aq) + I2(aq)
State and explain the trend in oxidising ability of the group 7 elements
Oxidising ability of the halogens decreases down the group. This is because the halogens must gain electrons when they react. This becomes harder as you go down the group because the number of shells/shielding/atomic radius increases so the electron is further away from the nucleus and experience less attration.
List the observations for the reactions of chlorine/bromine/iodine water with potassium chloride/bromide/iodide
There is no reaction with iodine water.
Explain why chlorine is added to drinking water
To sterilise it/kill pathogens/bacteria.
Write an equation for the addition of chlorine to water. Which product kills bacteria
CL2 + H2O > HCLO + HCL
- chlorate ions (ClO-) kills pathogens as it is a powerful oxidising agent.
Write two equations for the addition of chlorine to water in the presence of sunlight.
What is the main chemical in household bleach? Write an equation for its formation from chlorine
2NaOH(aq) + Cl2(g) à NaCl(aq) + NaClO(aq) + H2O(l). The chlorate ions (ClO-) is the active ingredient as it is a powerful oxidising agent.
Write a half equation to show how chlorate(I) behaves as an oxidising agent
ClO- + H2O + 2e- à Cl- + 2OH-
State and explain the trend in reducing ability of the halides
The halides become stronger reducing agents as you go down the group. This is because they lose electrons when they react. This becomes easier as they have more shells/energy levels/shielding as there is less attraction from the nucleus.
Write an equation for the reaction of sodium chloride with sulfuric acid. State the observations made during this reaction
NaCl(s) + H2SO4(l) à NaHSO4(s) + HCl(g). Misty fumes of HCl
Write two equations for the reaction of sodium bromide with sulfuric acid. State the observations made during these reactions
NaBr(s) + H2SO4(l) à NaHSO4(s) + HBr(g). Misty fumes of HBr
2H+ + 2Br- + H2SO4 → SO2 + 2H2O + Br2 . Brown fumes of Br2
Write two equations for the reaction of sodium iodide with sulfuric acid. State the observations made during these reactions
NaI(s) + H2SO4(l) à NaHSO4(s) + HI(g). Misty fumes of HI.
8H+ + 8I– + H2SO4 à H2S + 4H2O + 4I2. Purple fumes/black ppt of I2, Colourles gas with bad smell of H2S. Colourless gas with choking odour of SO2, Yellow precpitate of S
Describe the chemical test for halide ions (including use of ammonia)
First add silver nitrate and nitric acid. The silver ions form precipitates of silver halides (i.e. Ag+(aq) + I-(aq) à AgI(s)). AgCl is a white precipitate, AgBr is a cream precipitate and AgI is a yellow precipitate. Dilute ammonia will dissolve AgCl (AgCl(s) + 2NH3(aq) → Ag(NH3)2+(aq) + Cl−(aq) ) and concentrated ammonia will dissolve AgBr (AgBr(s) + 2NH3(aq) → Ag(NH3)2+(aq) + Br−(aq) )
State and explain which type of acid is used in the chemical test in Q16
Nitric acid must be used as both hydrochloric acid and sulfuric acid will create precipitates with the silver ions.
Halide ions using sulfuric acid
Halide ions using silver nitrate
Carbonate ions
Carbonate ions: add a strong acid. Effervesce of CO2 will be observed (2H+(aq) + CO32-(aq) à CO2(g) + H2O(l)). If the CO2 is bubbled through limewater, it turns cloudy/milky.
Sulfate ions
Sulfate ions: Add barium chloride or barium nitrate. A white precipitate of barium sulfate is formed. Ba2+ (aq) + SO42- (aq) à BaSO4(s)
Hydroxide ions
Hydroxide ions: use red litmus paper (turns blue) or Universal Indicator paper (turns blue/purple)
Ammonium ions
Ammonium ions: add sodium hydroxide to turn ammonium ions into ammonia gas: NH4+(aq) + OH-(aq) à NH3(g) + H2O(l). Test the ammonia gas by using damp red litmus paper (turns blue) or damp Universal Indicator paper (turns blue/purple).
Group 2 ions (using sodium hydroxide)
Group 2 ions (using sodium hydroxide): Group 2 hydroxides are formed i.e. Mg2+ (aq) + 2OH-(aq) à Mg(OH)2(s). Beryllium and magnesium hydroxide are insoluble so form white precipitates, the rest are soluble so form colourless solutions.
Group 2 ions (using sulfuric acid)
Group 2 ions (using sulfuric acid): Group 2 sulfates are formed i.e. Ba2+ (aq) + SO42- (aq) à BaSO4(s). Calcium, strontium and barium sulfates are insoluble so form white precipitates, the rest are soluble so form colourless solutions
